Schoch Bradley, Hast Michael W, Mehta Samir, Namdari Surena
Department of Orthopaedic Surgery, University of Florida, Gainesville, Florida.
Biedermann Lab for Orthopaedic Research, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.
JBJS Rev. 2018 Jan;6(1):e6. doi: 10.2106/JBJS.RVW.17.00049.
Locking plate fixation strength relies on axial alignment of the screw axis and plate hole, with small deviations in alignment substantially decreasing the load to failure. In an effort to overcome this technical deficiency, polyaxial locking plates were designed to provide increased flexibility of screw positioning with the intent of not sacrificing fixation strength. The purpose of this article is to review the variety of polyaxial locking mechanisms currently available, to compare the biomechanical performance of these designs, and to highlight their differences, which may have clinical implications.
A systematic review using the search terms "polyaxial locking," "variable angle locking," "polyaxial screws," and "variable angle screws" was conducted to identify all English-language articles assessing variable-angle locking screw technology. All articles directly comparing the biomechanical performance of polyaxial locking technologies were included.
Polyaxial locking is achieved by 5 described mechanisms: point-loading thread-in, cut-in, locking cap, expansion bushing, and screw-head expansion. With increasing insertion angulation, point-loading thread-in and cut-in designs demonstrate reduced failure strength. However, locking-cap fixation maintains consistent failure strength with increasing off-axis insertion angles.
Reports comparing polyaxial locking technologies are limited. The current biomechanical literature raises concerns that these mechanisms have various strengths and performance characteristics. Based on the results of the few studies that exist, it appears that locking-cap fixation provides superior biomechanical strength when compared with point-loading and cut-in designs. Additional studies are needed to assess variable-angle locking mechanisms more completely.
锁定钢板的固定强度依赖于螺钉轴线与钢板孔的轴向对齐，对齐上的小偏差会大幅降低破坏载荷。为克服这一技术缺陷，设计了多轴锁定钢板，以在不牺牲固定强度的情况下增加螺钉定位的灵活性。本文的目的是回顾当前可用的各种多轴锁定机制，比较这些设计的生物力学性能，并突出它们可能具有临床意义的差异。
进行了一项系统综述，使用搜索词“多轴锁定”“可变角度锁定”“多轴螺钉”和“可变角度螺钉”来识别所有评估可变角度锁定螺钉技术的英文文章。纳入所有直接比较多轴锁定技术生物力学性能的文章。
多轴锁定通过5种描述的机制实现：点加载螺纹旋入、切入、锁定帽、膨胀衬套和螺钉头膨胀。随着插入角度增加，点加载螺纹旋入和切入设计的破坏强度降低。然而，锁定帽固定在离轴插入角度增加时保持一致的破坏强度。
比较多轴锁定技术的报告有限。当前的生物力学文献引发了对这些机制具有不同强度和性能特征的担忧。基于现有少数研究的结果，与点加载和切入设计相比，锁定帽固定似乎提供了更好的生物力学强度。需要更多研究来更全面地评估可变角度锁定机制。
